Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems. Wireless Local Area Networks (WLANs), such as Wi-Fi (IEEE 802.11) networks are also widely deployed and used.
Generally, a wireless multiple-access communications system may include a number of base stations or access points, each simultaneously supporting communication for multiple mobile devices. Base stations or access points may communicate with mobile devices on downstream and upstream links. Each base station or access point (AP) has a coverage range, which may be referred to as the coverage area of the cell. Wireless communication between base stations and mobile devices may include high data rates. In such situations, the performance of a wireless communication system is mainly governed by the wireless channel environment. High data rate transmission and high mobility of transmitters and/or receivers usually experiences challenging frequency-selective and time-selective fading channel conditions. Mitigating such fading conditions results in an efficient data transmission.
Accurate estimate of channel state information (CSI) impacts the performance of a wireless communication system. In contrast to the typical static characteristics of a wired channel, the wireless channel may be dynamic and change quickly. Orthogonal frequency division multiplexing (OFDM) has been conventionally adopted for a wide range of wireless and wireline applications. The major virtues of OFDM include its resilience to multipath propagation, the possibility of achieving channel capacity, and the availability of frequency diversity scheduling in multiuser communication systems. However, although the OFDM based transmission has become the physical layer for broadband communications, it suffers from several drawbacks including a large peak-to-average power ratio (PAPR), intolerance to amplifier nonlinearities, and high sensitivity to carrier frequency offsets. As a result, implementation of an OFDM system to transmit data across a wireless channel may not be optimal for certain wireless systems.
An alternative approach to OFDM systems focuses on Cyclic Prefix (CP) single-carrier (SC) modulation techniques. While a CP based single-carrier transmission system with frequency-domain equalization may provide a lower peak-to-average power ratio than an OFDM system, the CP based SC systems may suffer from poor channel estimation with comparable or even high implementation complexity against OFDM system in a fast-variant channel environment. Therefore, adoption of CP based SC modulation techniques to assist with channel estimation may not be ideal. While both OFDM and SC modulation techniques provide certain unique advantages, each suffers from inherent drawbacks that negatively impact the performance of a wireless channel with respect to channel estimation and data transfer.